Fig. 3 Electron microscopy photographs: (a) TEM image of the toluene gel made of 2 (3 wt%), (b) TEM image of the toluene gel made of 2 (3 wt%) + 1b
(molar ratio 2 : 1b = 10 : 1), (c–f) SEM images of the sample (b), (d–f) enlarged views of individual nanobrushes in (c).
junction zones of higher density was observed under TEM without
staining (b). Interestingly, the observation of the xerogels under
SEM revealed the formation of a new morphological moiety along
thin strands with diameters of ca. 30 nm. The new induced
morphology bears a striking resemblance to laboratory brushes. In
most cases it is clearly seen that the individual nanobrushes are
formed by a twisted left-handed fibrillar backbone with a diameter
of ca. 25 nm and surrounding small left-helical fibers emerging
from the ends of the fibrillar spine (Fig. 3f). The same type of
nanoscale structures could be also found with the other Zn(II)-Pcs
Notes and references
1
Y. Osada and A. R. Khokhlov, Polymer Gels and Networks, Marcel
Dekker, New York, 2002.
2
J. H. van Esch and B. L. Feringa, Angew. Chem., Int. Ed., 2000, 39,
2263–2266; O. Gronwald and S. Shinkai, Chem.–Eur. J., 2001, 7,
4328–4334; R. G. Weiss and P. Terech, in Molecular Gels. Materials
with Self-Assembled Fibrillar Networks, Kluwer Academic Press,
Dordrecht, 2006.
3
T. Kato, Science, 2002, 408, 2414–2418; J. H. Jung and S. Shinkai, Top.
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4
5
6
7
(1a, 1c) although in an appreciably lower concentration per surface
2002, 7, 148–156.
unit. The (R)-chiral centers in 2 induce the anti-clockwise helicity
H. Ihara, M. Takafuji and T. Sakurai, Encycl. Nanosci. Nanotechnol.,
2004, 9, 473–478.
X. Huang, P. Terech, S. R. Raghavan and R. G. Weiss, J. Am. Chem.
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M. Kimura, T. Kitamura, T. Muto, K. Hanabusa, H. Shirai and
N. Kobayashi, Chem. Lett., 2000, 1088–1089.
12
of the strands, in good agreement with previous observations.
We believe that the induced morphological variations could be
useful as well to control the catalytic and photophysical functions
of the MPcs. Generally strong aggregates of MPcs tend to exhibit
a blue shift, and due to selection rules these species are non-
fluorescent. However, another possible geometry is the clamshell
arrangement, whereby the Pc molecules are held over one another
but the rings are no longer parallel and emission is not
categorically excluded.{ In fact, such an orientation effect could
occur in the case of the gel made of 2 + 1c in toluene, which was
characterized by a short lifetime (t = 1.1 ns) and low quantum
8 K. Ohta, T. Watanabe, T. Fujimoto and I. Yamamoto, J. Chem. Soc.,
Chem. Commun., 1989, 1611–1612; T. Ishi-I and S. Shinkai, Top. Curr.
Chem., 2005, 258, 119–160 and references therein.
9
R. Litran, E. Blanco, M. Ramirez-del-Solar, A. Hierro, M. A. Diaz-
Garcia, A. Garcia-Caba n˜ ez and F. Agullo-Lopez, Synth. Met., 1996, 83,
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1
0 H. Engelkamp, S. Middelbeek and R. J. M. Nolte, Science, 1999, 284,
85–788 and references therein.
1 (a) J. A. Duro and T. Torres, Chem. Ber., 1993, 126, 269–271; (b)
7
yield (W
f
= 0.37).{ The fluorescence intensity of the gel remained
virtually unchanged while increasing the concentration of an added
1
E. M. Garc ´ı a-Frutos, F. Fern a´ ndez-L a´ zaro, E. M. Maya, P. V a´ zquez
and T. Torres, J. Org. Chem., 2000, 65, 6841–6846; (c) A. de la
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2
+
electron transfer quenching reagent (MV ) up to 2.5 mM,{
suggesting an absolute reduction in collisions between 1c and
2+
7
MV through incorporation into nanofibrous assemblies. No
accurate fluorescence data were obtained for gels containing 1a–b.
In summary, we have reported the physicochemical character-
ization of new optical active organogels made by simple
association of a bis(amide)cyclohexane-based LMOG with a series
of octakis(alkyloxy)-substituted Zn(II)-Pcs, which revealed a
noteworthy stabilization and morphological effect. We are
currently continuing our experiments involving lyotropic MPcs,
which will allow us to study the effect of the supramolecular
environment created by an LMOG on the liquid crystalline
1
2300–12308; (d) D. M. Guldi, A. Gouloumis, P. V a´ zquez, T. Torres,
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007, 2000 and references therein.
2 K. Hanabusa, M. Yamada, M. Kimura and H. Shirai, Angew. Chem.,
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1
1
3 J. A. Duro, G. de la Torre, J. Barbera, J. L. Serrano and T. Torres,
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15 R. Greco, in Advanced Polymeric Materials, CRC Press LLC,
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1
16
properties of the MPcs, if any, and vice versa.
Funding by MEC (Spain-CTQ2005–08933/BQU), Comunidad
de Madrid (Spain S-0505/PPQ/000225) and EU (Solar-N-type,
MRTN-CT-2006-035533) is gratefully acknowledged. D.D.D.
thanks the Spanish MEC for a RyC contract.
1
This journal is ß The Royal Society of Chemistry 2007
Chem. Commun., 2007, 2369–2371 | 2371